The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
A typical internal combustion engine is a combination of systems that individually serve a specific function. The air intake system provides throttled air to the engine. The fuels system stores, transports, and regulates fuel flow into the combustion chambers of the engine. The ignition system provides spark for igniting the air/fuel mixture. The power conversion system converts the chemical energy of combustion into work that is transferred to the tires of the vehicle. Other systems perform functions that improve fuel economy and emissions, cool the engine and provide heat to the vehicle cabin, or run other accessories such as power steering or air conditioning.
The size of the engine is typically tailored to the size and purpose of the vehicle. For example, a small light car built for fuel efficiency may include a small three cylinder or four cylinder engine with 1.5 to 2.0 Liters of displacement. Alternatively, a full-size pick-up truck or van that is purposely built for carrying tools and pulling machinery will require an engine having a larger displacement and more cylinders. A displacement of 4.5 L and above in a V8 or V10 configuration provides the torque and power required to carry and pull heavy loads, such as when the vehicle is operated in tow/haul mode. However, there are occasions of use when such a vehicle will not require all of the torque available in the V8 or V10 engine. It is during such occasions that it becomes desirable from a fuel efficiency standpoint to deactivate or simply not use all of the cylinders that are available. Thus, a method of operating the engine has been developed to improve fuel economy while maintaining the overall capacity of torque available to the vehicle operator.
Active fuel management methods have been developed which include shutting off fuel delivery to a cylinder when the torque demand on the engine is low. However, there are many issues with controlling an engine and powertrain when using active fuel management. Drivability, torque demand, Noise and Vibration must all be maintained or improved while at the same time improving fuel economy.
It is appreciated that when engine cylinders are deactivated with active fuel management methods that pumping losses associated with those cylinders are eliminated. These pumping losses directly affect the braking (negative) torque capacity of the engine, i.e., reducing the number of active cylinders directly reduces engine braking capacity which can allow the vehicle to coast longer distances. In some instances during active fuel management operation, it may be desirable to vary the level of engine braking capacity which could be beneficial under certain driving conditions.
Thus, while current active fuel management controls achieve their intended purpose, the need for new and improved active fuel management controls which ensure the vehicle operators expectations and desires are achieved is essentially constant.